The present invention relates to a method of separating cobalt (II) and nickel (II) by extraction from water solutions containing these metallic ions.
So far, the number of methods for technological separation of cobalt and nickel by extraction is very limited. The best known methods are based on the ability of cobalt to form chloride complexes, whereby the cobalt can be extracted selectively from a strong chloride solution by means of anion-exchange type extraction reagents, such as amines. Since nickel does not form corresponding chloride complexes, the separation of cobalt and nickel is very sharp, but there is a disadvantage in the corrosion problems caused by strong chloride solutions and the change of environment required in most cases, i.e., from a sulphate solution into a chloride solution.
Another group of extraction processes is based on the use of ammonia complexes (e.g. U.S. Pat. Nos. 3,276,863; 3,380,801; and 3,438,768 and Finnish Patent Application No. 203/71. In some of these processes, the cobalt has been oxidized into a trivalent form, while in others the separation is carried out while both the metals are bivalent.
On the other hand, very little is known about the separation of cobalt and nickel from acid solutions. U.S. Pat. No. 3,336,133 describes the use of acid thio-sulphates for the extraction of nickel from cobalt-bearing solutions, and Finnish Patent Application No. 1892/72 introduces an extraction process using an extraction agent mixture. U.S. Pat. No. 3,399,055 introduces a process for extracting cobalt from a nickel-bearing solution by means of an organic phosphoric acid.
The object of the present invention is to provide an improved separation of cobalt and nickel from each other from water solutions which contain both cobalt and nickel. The process according to the invention does not set any special requirement for the quality of the anion in the solution, but the extraction can take place from, for example, sulphate, nitrate, or carbonate solutions.